The present disclosure relates to video coding devices and systems, and to search algorithms employed in conjunction with such devices.
Digital-based electronic media formats have become widely accepted. Digital compact discs (CDs) and audio files, such as MP3s (MPEG Audio—layer 3), are now commonplace. Video media, however, has been slower to transition to digital storage and digital transmission formats than audio media. One reason for the slower integration of digital video media formats into the marketplace is the volume of information required to accurately produce video of an acceptable quality from a digital representation. Additionally, encoding and decoding video in a digital format consumes substantial system resources and requires systems capable of processing information at high speeds. Further, the large amounts of information used to represent digital video also necessitate high-bandwidth transmission systems and high-capacity storage systems.
The development of faster computer processors, high-density storage media, and efficient compression and encoding algorithms have led to more widespread implementation of digital video media formats in recent years. The Digital Versatile Disc (DVD) has rapidly replaced video cassettes as the primary storage media for video due to its high image quality, very high audio quality, convenience, and added functionality. Further, the digital Advanced Television Standards Committee video transmission system is in the process of replacing the analog National Television Standards Committee transmission system.
Computer systems have been using various digital video formats for a number of years. Specifically, computer systems have employed many different methods for compressing and encoding or decompressing and decoding digital video. A video compression/decompression method, implemented using hardware, software, or a combination of hardware and software, is commonly referred to as a CODEC. A number of popular digital video compression and encoding systems have been developed based on the standards propounded by the Moving Picture Experts Group (MPEG), including the MPEG-1, MPEG-2, and MPEG-4 standards. Video CDs and early consumer-grade digital video editing systems use the MPEG-1 digital video encoding format. DVDs, video games, and some direct broadcast satellite systems are encoded in accordance with the MPEG-2 standard. MPEG-4 is now being used to deliver DVD (MPEG-2) quality video at lower data rates and smaller file sizes, and thus enables digital video playback on products ranging from satellite television systems to wireless devices.
The MPEG standards set forth methods for compressing a series of images, such as frames or fields, and for encoding the compressed images into a digital bit stream. When a video image is encoded in an MPEG system, the video image is divided into multiple pixel arrays, such as 8×8 pixel blocks or 16×16 pixel macroblocks. Each pixel array can then be independently compressed and encoded.
When performing compression using an MPEG coder, such as a coder that is in compliance with the MPEG-2 or MPEG-4 standard, images may be encoded using three picture types. Specifically, images may be encoded using I-pictures, P-pictures, and B-pictures. I-pictures are encoded with reference only to the information within the picture, and thus may be decoded without reference to any other pictures. P-pictures are encoded with reference to preceding pictures, and thus permit the use of motion compensation to provide for a greater degree of compression. B-pictures are encoded with reference to succeeding pictures, and also permit the use of motion compensation. Because B-pictures are decoded using succeeding pictures, however, some reordering of the sequence of decoded pictures is required prior to display.
Digital video systems have also been developed based on standards other than those published by MPEG. For example, similar standards have been circulated by other organizations, such as the H.261-H.264 standards developed by the International Telecommunication Union. Additionally, proprietary codecs have been developed by other organizations and individuals. For example, Compression Technologies, inc. produces digital video compression tools based on the Cinepak codec and DivXNetworks produces a variety of applications based on the DivX codec. These standard and proprietary codecs represent only a few of the many different ways to compress and encode digital video information.
FIG. 1 presents a media sequence 10, such as a portion of a movie. The media sequence 10 can be organized as a track 12 of digital video information that can include one or more image segments, such as the first image segment 14 and the second image segment 16. In turn, each image segment is comprised of one or more samples, such as frames of image data. The track 12 also can include one or more empty segments 18, which are not associated with any video information and during which no video information is presented. In addition to the track 12 of digital video information, the media sequence 10 also can include a track of audio information and a track of text information (not shown).
The track 12 of digital video information represents the movie timescale and the image segments included in the track 12 are sequentially ordered with respect to time. Therefore, the first image segment 14 in the track 12 is temporally ordered such that it precedes the second image segment 16. During forward play, the first image segment 14 will thus be displayed prior to the display of the second image segment 16. As with the image segments, each of the empty segments 18 included in the track 12 is temporally ordered with respect to the other segments.
The order of the image segments and the empty segments included in the track 12 is defined in an edit list 20. For each image segment and empty segment included in the track 12, there is a corresponding entry, or edit, in the edit list 20. Each edit defines parameters associated with the image segment or the empty segment to which it corresponds. For example, an edit identifies the point in the movie timescale at which the corresponding image segment or empty segment is to begin. The edit also identifies the duration, expressed in terms of the movie timescale, over which the corresponding image segment or empty segment will be played. Further, with respect to image segments, an edit identifies the rate at which the corresponding image segment is to be played back. A playback rate of 1.0 can be associated with the first image segment 14 to indicate that playback should occur at a rate equal to the timing information associated with the first image segment 14. Similarly, a playback rate of 2.0 can be associated with the second image segment 16 to indicate that playback should occur at a rate equal to twice the timing information associated with the second image segment 16.
The one or more samples comprising each of the image segments included in the track 12 are contained in the media 22. If the edit list 20 is modified to insert an additional image segment into the track 12 after the media 22 has been populated, the samples comprising the newly added image segment are also entered into the media 22. It is also possible to delete an image segment from the track 12 during editing, but the samples comprising the deleted image segment are not removed from the media 22. Once a sample has been added to the media 22, its intrinsic properties cannot be modified and the sample cannot be removed from the media 22. The media 22 thereby ensures that every sample associated with an image segment previously identified in the edit list 20 will be available if it is ever required in connection with the track 12.
The media 22 also incorporates the concept of a media timescale, which is a positive integer. The media can be subdivided into X units of media time, where X is a positive integer. The duration of each unit of media time can then be determined to be X÷(media timescale). As described above, the media 22 contains every sample associated with an image segment that has previously been inserted into the track 12. Therefore, the media 22 can be ordered as a sequential list of samples 24, wherein each sample is assigned a unique sequence number. For example, the first sample 26 in the list of samples 24 can be assigned sequence number 1. A sample duration 28 also is associated with each sample in the list of samples 24, indicating how long, in media time, a given sample will be displayed. Sample durations, which are expressed as positive integers, may differ among different samples in the media 22. The media duration 30, in turn, is equal to the sum of the sample durations for all of the samples included in the media 22.
The first sample 26 included in the media 22 has a sample time of zero, which also represents the zero point of the media timescale. The second sample 32 included in the media 22 has a sample time equal to the first sample duration 28, because the sample time of the first sample 26 is zero. Each subsequent sample included in the list of samples 24 has a sample time equal to the sum of the sample time of the preceding sample and the duration of the preceding sample. Therefore, the samples included in the media 22 partition the media time for the entire media duration 30 without any gaps. The structure of the list of samples 24 cannot be adapted to permit the use of B-pictures, however, as it does not separately account for decode times and display times.